Join Date: Nov 2009
Location: Ontario, Canada
because it's more of a waveguide. Doesn't really provide the acoustic impedance benefit of a horn.
This is an old saw which has been hacked to death by the likes of Earl Geddes, Wayne Parham, and David Smith.
Granted, the SEOS waveguides *are* too short, which causes measurable response ripple in the passband. Most people who use them find that they are very nice, and the ripple can be effectively dealt with in the crossover design, and/or with careful EQ. Mr. Parham may differ on that opinion.
But simply put, a constant directivity horn has very simple mathematical constraints. Conical. With allowances for throat and mouth transitions. Earl Geddes will say: Oblate Spheroidal. But OS is as near as Damn! is to swearing, to conical overall. The refinements are in the curve which matches the driver exit angle to the horn angle, for the most part. Pardon me, Earl, for over-simplifying.
So, some basic Trig will define the horn proportions. A 90 degree horn will be twice as wide as it is deep. +/- minor fudge factors.
The "acoustic impedance benefit of a horn"-- sorry, this has been debunked many times over. The lower usable frequency limit of a horn is determined solely by the mouth dimension. A 12" horn is good down to 1kHz. A 24" horn is good down to 500Hz, as a rule of thumb. Any nonsense about flare rates and acoustic impedance benefits is just that, nonsense. The only thing that is affected is directivity.
To clarify, I am talking about horns which operate in the range above the Schroeder frequency of the room. Bass horns are a different animal, directivity is irrelevant, and the concept you refer to does, in fact, apply.
Last edited by Rational35; 9th October 2018 at 07:40 AM.